The problems that arise in generators for arc welders are linked mainly to the low power factor of the current absorbed from the power supply mains.
Additionally, another factor that has a negative effect on the efficiency of an arc welder provided according to known layouts and methods is the unpredictable variation of the power supply voltage.
With reference to the background art by way of example, the classic widely used layout of an electronic welder is shown in FIG. 1.
The layout comprises, on the mains side, a first rectifier stage 1 constituted only by diodes, followed by a bank of leveling capacitors 2.
The current thus rectified and leveled supplies an inverter block 3 provided by means of high-frequency electronic switches, which supplies the primary winding of a transformer 4.
The secondary winding of the transformer 4 is followed by a second rectifier stage 5.
The current in output from the second rectifier stage 5 is leveled by an inductor 6 and supplies a welding arc 7.
A generator of this kind, during operation, absorbs from the mains a current that has a behavior of the type shown in FIG. 2.
It is immediately evident that a waveform of this type has a high harmonic content, and this entails a low power factor.
In this situation, in order to have a high useful power level in the arc it is necessary to absorb a high RMS value from the mains.
This entails a considerable negative impact on the power supply network, since the high harmonic content and the high RMS value of the absorbed current cause an increase in the heating of the power supply conductors and a considerable distortion of the waveform of the voltage of the power supply line, which in turn causes an increase in losses in the ferromagnetic cores of the transformers connected thereto.
Additionally, the distortion of the waveform introduces considerable noise on the line.
Further, when the welding generators are of limited power, as occurs for those intended to be supplied by domestic utility systems, the high intensity of the absorbed RMS current causes the intervention of the thermal protection of the utility system even though the power delivered on the welding arc is lower than that of an equivalent resistive load.
Moreover, as already mentioned, a generator with a layout of the type shown in FIG. 1 inevitably is affected by the variations in the input supply voltage, and this reduces considerably the performance of said generator.
In view of these problems, welding generators have been devised that have additional stages that allow a mains current absorption that is as sinusoidal as possible, i.e., render the generator equivalent to a resistive load so as to be able to use all the active power available to the user.
Additional stages have also been adopted which have the task of automatically adapting the generator to the mains voltage variations, ensuring good and stable performance of the generator.
Generators with layouts of this type can be of the type shown schematically in FIG. 3.
This layout clearly shows that with respect to the diagram of FIG. 1 there is the addition of a stage 8 that is interposed between the rectifier block 1 and the leveling block 2.
This stage, termed PFC, can be provided in various kinds.
Generators of this type are in any case expensive and complicated and sometimes critical in the choice of the components that need to withstand high voltages.